


just one day, swear

by Kittenixie



Series: addition [1]
Category: Deltarune (Video Game), Undertale (Video Game)
Genre: Alternate Universe - Canon Divergence, Canon-Typical Violence, Gen, Ghosts, Possession, Sharing a Body, actually high key this time, but this is kind of self indulgent ngl :pensive:, i can't tag a ton bc i don't want to spoil stuff, universe hopping
Language: English
Status: Completed
Published: 2018-11-13
Updated: 2018-11-13
Packaged: 2019-08-23 08:06:18
Rating: Teen And Up Audiences
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 2,259
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/16615118
Author URL: https://archiveofourown.org/users/Kittenixie/pseuds/Kittenixie
Summary: Kris wakes up to find their body is not their own.





	just one day, swear

**Author's Note:**

> hi this is really self indulgent because i Needed it
> 
> forgot to put this here but [i have a deltarune/undertale discord server feel free to join that here](https://kittenixie.tumblr.com/post/179840597289/hi-i-made-a-deltaruneundertale-server-were)

Kris slumped into bed with a wide yawn, quickly shoving themself under the blanket with a sigh. They rolled over onto their side, effectively burritoing themself, and relaxed. Tomorrow was another school day, another day to hang out with their friends, maybe they'd go to the dark world with Susie. They found they had a lot more to look forward to lately. They hadn't had that since Asriel left for college. It was nice.

They laid in bed for a good while, eyes closed, but not quite able to sleep. Something felt off, and the feeling remained no matter how much they tried to brush it off. Still, eventually, they fell asleep.

As soon as morning came, they had a full-body spasm, then another, and another as they tumbled out of the bed. They hit the ground with a soft thud, then unsteadily, shakily got to their feet. They touched their face, their hair, their sweater, looked around at everything in the room as though getting their bearings.

The odd thing was that it wasn't Kris. They'd been forced into the situation of a backseat driver in their own car when they don't know who's actually driving. They weren't in control of their body. As soon as they realized this, they, of course, started to struggle. The thing controlling their body made a small grunt, tone unfamiliar in their mouth. 

“Just one day,” it spoke softly. “Promise. Swear.” Kris paused in confusion. It talked to them. What the hell did that mean? ‘Just one day’. Either way, they couldn't do much. The creature went around their room, meticulously examining everything. Oddly enough, it did a long pause after it looked at a picture of Asriel, eyes wide in surprise. Then it just turned away, frowning, and went back to looking around. It even found their knife, which it made a point to examine thoroughly before sticking it in their bag.

‘Why?’ They asked silently. If it heard, it didn't answer.

It liked to touch things, they were beginning to notice. It ran its fingers through their hair, pet their blankets, ran their hands along walls, picked things up just to feel. It was odd. Why? They had no idea.

Eventually, it got tired of the bedroom, picked their bag up, and went out into the hall. It took the time to look in a mirror, considering itself for a good few minutes. It reached up and tucked Kris’s bangs back, looking at their red eyes. Kris jolted slightly. ‘Don't do that.’ It paused for a few moments, then brushed their bangs back down. Whether it'd heard them or not was anyone's guess.

Mom soon came up to wake them, surprised to find them awake and actually checking their appearance for once. “Oh, my child! It is good to see you awake so early!” The creature piloting their body froze, staring up at the boss monster with wide eyes. Silently, they wrapped their arms around her in a hug. She seemed surprised, but quickly lifted them up, holding them close. The being sniffled, tears dripping down their cheeks. “Kris? Is everything alright, my child?”

“Y-Yeah, jus’... had a nightmare,” it mumbled. To Kris’s surprise, she didn't notice their odd mannerisms very much. “I'm alright.”

“That is good.” She cleared her throat, set them back down, and smiled. “Well, you still have plenty of time until we must leave. Usually I have to pry you out of bed,” she mumbled, blinking twice. Still, she didn't pay it much mind.

It went to go eat breakfast.

 

* * *

 

Yet another oddity about this thing, it really savored its food. It ate slow, enjoying every bite, and they even felt it holding back more tears. What was with this thing? It was just a pie.

Eventually, they got in the car to go to school. The thing stared out the widow peacefully, watching the world go by in silence. Kris slowly came to a realization.

‘Susie is gonna mess you up.’ The creature paused, blinking twice. ‘Crap, Susie is gonna mess  _ us _ up! Your acting is awful!’ It was a wonder that it even got past Mom. It blinked again, eyes narrowing, moving so its reflection showed in the glass and giving itself a questioning look. A question for them. ‘She's my friend. She's going to know a hundred percent that you're  _ not me _ . This is gonna be a disaster!’

It still didn't seem very alarmed. Ugh. This was going to be so bad. Kris chose to just stew in the back of the thing’s mind, their warnings weren't doing much to stop them.

It was all too happy to hold Toriel’s hand during the walk in. Odd. Still, it headed into class with a smile on their face. Somebody would absolutely notice. Susie glancedat them after they sat, raising a brow. “You're in a good mood,” she commented dryly. It just nodded. Susie’s eyes narrowed.

‘She knows. She definitely knows. You're screwed. We are both screwed.’ It pointedly ignored Kris’s worrying, instead focusing on taking notes and doing their schoolwork. ‘How do you even like doing  _ school _ ? This is so stupid.’ They could've  _ sworn _ it let out a snort. Asshole.

Honestly, they worked like they were in a grade level or two higher, quickly finishing up their worksheet. Still, it seemed to enjoy doing it, somehow. This prick was going to get a better grade than them. ‘Ugh. Of course it's better at school than me.’ The thing flinched slightly, like it was stung. ‘...What?’

It looked around for a moment, then quickly wrote “they” on the corner of their paper. ‘Oh. Alright. I mean… sorry, I guess?’ They shrugged slightly in response, erasing the simple word and going back to taking notes. How weird.

The rest of the class was still working, they were already done. It was suspicious. They were usually one of the last. It wasn't like they were bad at school or anything, they just didn't care much and procrastinated a lot. This thing just did it in a few minutes. They rooted through Kris’s bag for a minute, head tilted. ‘Don't have any books.’ The creature pouted, instead choosing to just sit at their desk in silence. Susie’s eyes bored into the back of their head, but they ignored it.

The bell rang eventually, and they stood up. They flinched as they felt a strong hand on their shoulder. They turned around, and Susie glared at them. “Let's walk, ‘ _ Kris _ ’,” she practically ordered.

“Oh.” They paused. “...Alright.”

‘We're dead,’ Kris mourned inwardly, though the one in their body ignored them again. Susie half-led, half-dragged them across the school, stopping near the familiar supply closet.

“What is  _ up _ with you today?” She questioned, slight growl to her voice. “You're acting real off, Kris.”

“I dunno what you mean. I'm normal as ever,” they replied with a shrug. “Nothin’s wrong.” Susie narrowed her eyes, then grabbed the front of their collar, lifting them up to narrow her eyes in their face.

“That's not how Kris  _ talks _ . Spill before I spill your damn  _ guts _ .” Both they and the one in their body shuddered. Kris knew she wouldn't. Their uninvited guest did not. They reached back, gripping something in their pocket.

Their knife.

_ ‘Don't! _ ’ Kris hissed, trying to force their control back in. As a result, they got the knife out, but ended up with it frozen out in the open. Susie growled, grabbing it and tossing it across the floor.

Susie glared, then opened her mouth wide, threatening yet again to crush their head in her sharp teeth. The one controlling them started flailing violently, though Susie didn't let them hit anything. She suddenly dropped them on the floor. A familiar routine. The one in their body sat there for a few moments, breathing heavily in a panic, then slowly stood, wheezing. Still, they looked up and met Susie’s glare with one of their own, defiant.

Susie’s eyes narrowed. “If they're not back by tomorrow, I'm snapping your head off your shoulders,” she warned pointedly. “Got it?” The creature glared for another moment, then nodded silently. “Good.” Without another word, she walked off.

They went and picked up their knife, glaring into the shiny steel. “You could've got us killed,” they hissed out, eyes narrow.

‘No. She wouldn't do that.’

“Would've been nice to know.” They tucked their knife away, then stormed out of the school. What was their damage?

 

* * *

 

 

The thing made a point to explore to their heart’s content, looking at everything in town and speaking to everyone, too. They stopped at the library for a little while, reading a book about something called “soul theory”. Kris pretty much ignored all of it. The thing didn't care.

It was getting late when they got home, though Mom didn't mind-- that was becoming more and more normal for them after the dark world incident. The thing gave her one last long hug, ate one more pie slice, and left to their room.

As soon as they went in, their guard dropped. Kris instantly seized the moment, taking it to grab control back, rip the unwelcome soul out of their chest, and toss it full speed into the birdcage in the corner of the room, the force of it causing the cage to shut. They heard a low wheeze, and an oddly transparent boss monster appeared next to the wagon, frowning.

“ _ That was kind of uncalled for.” _

“You possessed me!” Kris replied defensively.

“ _ Yeah, but still. _ ”

Kris pressed a palm to their face, sighing deeply. “Okay. What's your deal.”

“ _ Don't know what you mean.” _

“Dude.” Kris made a vague gesture, irritated. “Look. You didn't hurt me. You didn't really… Do anything bad. If you need help, I can try, but you have to tell me what's going on.”

The ghost hesitated. “ _ Really?” _

“Really.”

Another pause. They got more comfortable on the floor. Could ghosts be comfortable or uncomfortable? They didn't know. “ _...I'm… okay. This is going to be really unbelievable.” _ They took a deep breath. “ _ I'm from another universe. Vaguely like this one, but still different. Me and a friend, we kind of… We messed up, but we went back and fixed everything. And then I got sent to the void. _ ” A pause, and they glanced at Kris to make sure they weren't losing them. “ _...I was stuck there for a while. I don't know how long. I got out and got sent here, to you. I wasn't sure if you'd just kick me straight out, so… I wanted to make sure I got one day. Just one. To be alive again, y’know?” _ It was certainly a weird one, but they'd take it. Except…

“So why are you so weird about my family?” The ghost looked away.

“ _ They were, um… My adopted family. In my universe. _ ”

“...Where'd they manage to find another boss monster?”

“ _ Oh. No. I was human.” _ They paused, concentrating, and their form changed. A human, probably a little younger than Kris, with brown, slightly curly hair and blushy cheeks. They blinked twice, red eyes fixing on them. “ _ I just like looking like my family. _ ”

“Yeah. I can understand that,” they replied sympathetically. “One time when I was little, I asked them when my horns would grow in, and they bought me fake ones. Made me so happy.” The ghost let out a laugh. “So, um… how exactly can I help you?”

The ghost paused for a few moments in thought. “ _...I need you to take me back for a little while. Won't do anything that'll hurt you, swear.” _

“Didn't think you would,” Kris replied easily, opening the cage. The soul came back to them, the projection of the ghost coming with it.

 

* * *

 

Light streamed through Kris’s bedroom window, shining on their face. Ugh, they must've forgotten to close it last night.

They glanced at the other side of the room, with Asriel’s bed and all his belongings. They missed him still, even if they talked online and they had friends to fill the void now. Still, he was making something of himself, and they couldn't be prouder.

They looked up, intending to stare at the ceiling, but instead their gaze met with an unfamiliar surface. It took them a minute or two to recognize it as the bottom of a second bunk. What?

Their door opened. “Kris, Chara! Wake up, my children! You will be late to school at this rate!” Toriel glanced inside, noticed that the curtain was already open, and left them be.

Chara?

They blinked, hearing a shuffling above them. A fluffy boss monster with brown-tipped ears hung down from the top bunk to blink at them, eyes shining happily. When Kris met their gaze, they smiled wide, obviously overjoyed. “Sorry, you don't get your room all to yourself anymore, huh?”

“That's, uh. That's alright,” they stammered, blinking rapidly. The boss monster-- ghost--  _ Chara _ \-- climbed down from the top bunk, practically bouncing with excitement.

“Come on! We'll be late!”

“Hold on, so are we siblings now?”

“Oh, uh. Yeah. Or at least, everyone thinks we are.” They shrugged. “Sorry. I couldn't think of another way to rewrite myself in, so. Are you alright with that?”

“Rewrite… Uh. Yeah, sure,” they replied, head tilted. Well, they didn't understand what Chara did, but they had a new goat sibling now.

“Cool. Now come on! We won't even get breakfast at this rate!” They ran out of the room before Kris could even respond. Kris sighed, shook their head in amusement, and walked out after them.

They'd done good.

**Author's Note:**

> okay now that that's done
> 
> i Might make another fic abt this because i actually really liked writing it? chara has been my favorite character for like years now and i missed writing them so much
> 
> feel free to ask questions abt this mess uwu
> 
> noteworthy changes/decisions  
> -struggled to decide whether chara should become kris's sibling or just some random other schoolkid who just showed up after the fact  
> -was originally going to be from chara's perspective, first through the whole thing and then just for the beginning, decided to scrap the idea  
> -thought about keeping their ghost appearance human the whole time but decided against  
> -considered more explanation abt What they did but y'know what? it's fine


End file.
